Pneumatic tire and method of producing the same

ABSTRACT

Disclosed is a pneumatic tire that includes a tread having a pattern asymmetrical about the tire equatorial plane, and that may reduce cavity resonance and has good steering stability. A pneumatic tire includes a tread portion having a pair of tread halves, the tread halves extending between the tire equatorial plane and respective outer ends in the tire width direction of the tread portion, respectively, and having different negative ratios. The tread portion has short fibers fixed to at least a portion of a tire inner peripheral surface of the tread portion, and one of the tread halves with a higher negative ratio has a higher short-fiber fixation area ratio than that of the other tread half.

TECHNICAL FIELD

This disclosure relates to a pneumatic tire and a method of producingthe same.

BACKGROUND

It is known that a pneumatic tire, due to structures thereof, exhibits acavity resonance phenomenon caused by the length of a circular tubeinside the tire. Further, a pneumatic tire, regardless of the type,generates noise having cavity resonance frequency in the range of 200 Hzto 270 Hz according to a circumference length thereof, and said noise isa main cause for unpleasant vehicle-interior noise.

As described above, since air resonance in the interior of the tire is ageneration factor of the vehicle-interior noise, a method for absorbingnoise in the interior of a tire is effective as an improvement method.Examples of conventionally proposed methods include, as disclosed inJP200482387A (PTL 1), a technique of adhering short fibers to a tireinner peripheral surface. This technique is characterized in that theadhesive used for a tire inner peripheral surface is dried to form anadhesive layer with high rigidity and, consequently, rigidity increasesat those portions to which short fibers are adhered.

Additionally, some passenger car tires adopt a tread having a patternasymmetrical about the tire equatorial plane, from the viewpoint ofabrasion resistance and the like. Such a tire has the problem that therigidity tends to decrease on the side of the tread pattern where thenegative ratio (the proportion of groove portions (portions notcontacting the ground) in the tread) is higher, and the rigidity tendsto be unbalanced in the lateral direction of the tread portion, with theresult that good steering stability may not be obtained. This alsoapplies to the tires with short fibers adhered to the tire innercircumferential surfaces as stated above.

CITATION LIST Patent Literature

PTL 1: JP200482387A

SUMMARY Technical Problem

It could thus be helpful to provide a pneumatic tire that is providedwith a tread having a pattern asymmetrical about the tire equatorialplane, and that can reduce cavity resonance and provide good steeringstability. It could also be helpful to provide a method of producing apneumatic tire that can efficiently produce such a pneumatic tire.

Solution to Problem

A pneumatic tire disclosed herein comprises a tread portion that hasshort fibers fixed to at least a portion of a tire inner peripheralsurface of the tread portion, and that has tread halves, in which one ofthe tread halves with a higher negative ratio has a higher short-fiberfixation area ratio than that of the other tread half.

In the pneumatic tire disclosed herein, the short fibers fixed to atleast a portion of the tire inner peripheral surface of the treadportion may reduce cavity resonance during driving and, furthermore,adhesive layers for fixing the short fibers can increase the rigidity ofone of the tread halves that has a lower rigidity, namely, a highernegative ratio, making it possible to correct the imbalance of rigiditybetween the tread halves and to achieve good steering stability.

As used herein, the term “tread” refers to a portion of a tire that ispresent in the tire radial direction, over a range in the tire widthdirection corresponding to a tread surface. Here, the term “treadsurface” refers to, for a tire assembled onto an applicable rim andfilled to a prescribed internal pressure, an outer peripheral surface ofthe tire around the circumference thereof that is formed by thoseportions (including groove portions, if any, formed in the outerperipheral surface of the tire) that are brought into contact with theroad surface when the tire is rotated under a load corresponding to themaximum load capacity. The above “applicable rim” refers to a standardrim (“Design Rim” in the YEAR BOOK of TRA below, and “Measuring Rim” inthe STANDARDS MANUAL of ETRTO below) specified by the standards below inaccordance with tire size, “prescribed internal pressure” refers to airpressure specified by the standards below in accordance with the maximumload capability, and the “maximum load capability” refers to the maximummass that the tire is allowed to bear according to the standards below.The standards are determined by valid industrial standards for theregion in which the tire is produced or used, such as the “Year Book” of“THE TIRE AND RIM ASSOCIATION, INC. (TRA)” in the United States ofAmerica, “The European Tire and Rim Technical Organization (ETRO)” inEurope, and the “JATMA YEAR BOOK” of “the Japan Automobile TireManufacturers Association (JATMA)” in Japan.

The aforementioned “negative ratio” refers to the proportion that grooveportions, namely, portions not contacting the ground, in a tread patternoccupy in the area of a target region on the tread surface.

The aforementioned “short-fiber fixation area ratio” refers to theproportion of the fixation area of short fibers per unit area of atarget region in the outer or inner peripheral surface of the tire.

As used herein, “negative ratio,” other tire dimensions, and the likeare intended to be measured for a tire assembled onto an applicable rimunder a prescribed internal pressure and under no-load condition.

A method of producing the aforementioned pneumatic tire disclosed hereincomprises: applying an adhesive to at least a portion of the tire innerperipheral surface of the tread portion; and adhering short fibers tothe portion to which the adhesive has been applied, wherein one of thetread halves with a higher negative ratio has a higher short-fiberfixation area ratio than that of the other tread half.

According to the method of producing the pneumatic tire, it is possibleto produce such a pneumatic tire in a more efficient way that has goodsteering stability and can suppress the generation of cavity resonance.

According to one of the disclosed aspects of the method of producing thepneumatic tire disclosed herein, after the applying, the short fibersare provided on the tire inner peripheral surface by electrostaticflocking. In this case, the short fibers may easily be fixed to the tireinner peripheral surface of the tire in a state where the short fibersstand upright thereon, which makes it possible to more efficientlyproduce a pneumatic tire that enables obtaining a noise-absorbingeffect.

Advantageous Effect

According to the disclosure, it is possible to provide a pneumatic tirethat comprises a tread having a pattern asymmetrical about the tireequatorial plane, and that may reduce cavity resonance and has goodsteering stability. According to the disclosure, it is also possible toprovide a method of producing a pneumatic tire that may produce such apneumatic tire in an efficient way.

BRIEF DESCRIPTION OF THE DRAWING

In the accompanying drawings:

FIG. 1 illustrates a part of the tread pattern of a pneumatic tiredisclosed herein according to one of the disclosed embodiments, where(A) is a top plan view and (B) is a cross sectional view in the tirewidth direction taken along line A-A;

FIG. 2 is a cross sectional view in the tire width direction of apneumatic tire of comparative example 2;

FIG. 3 is a schematic diagram illustrating a device for measuring cavityresonance and the principle thereof; and

FIG. 4 is a graph presenting measurement results of cavity resonance fortires of example 1, and comparative examples 1 and 2.

DETAILED DESCRIPTION

Intense study was made to investigate how to provide a pneumatic tirecomprising a tread having a pattern asymmetrical about the tireequatorial plane that can reduce cavity resonance and offer goodhandling stability, and a method that can efficiently produce such apneumatic tire. As a result, it was found that the imbalance of rigiditybetween the tread halves can be reduced when more adhesive layers arearranged in one tread half whose tread pattern has a higher negativeratio than the other. It was also discovered that the cavity resonanceof the tire can be reduced by arranging short fibers in the adhesivelayers. As a result, the pneumatic tire and method disclosed herein werecompleted.

The following describes the pneumatic tire and method disclosed hereinin detail with reference to the drawings. FIG. 1(B) is a cross sectionalview in the tire width direction of one embodiment of the pneumatic tiredisclosed herein. The pneumatic tire shown in FIG. 1 has a pair of beadportions 1; a pair of sidewall portions 2; a tread portion 3 continuedto the respective sidewall portions 2; a carcass 4 formed from onecarcass ply extending in a toroidal shape across the pair of beadportions 1 for reinforcing the bead portions 1, the sidewall portions 2and the tread portion 3; a belt 5 formed from two belt layers disposedon the outer side in the tire radial direction of the carcass 4 in thetread portion 3; a single belt reinforcing layer 6 disposed on the outerside in the tire radial direction of the belt 5; a bead filler 8disposed on the outer side in the tire radial direction of a bead core 7embedded in each of the bead portions 1; and an inner liner 9 disposedon the tire inner peripheral surface side of the carcass 4.

The carcass 4 of the example shown in FIG. 1 is formed from a singlecarcass ply and has a main body portion extending in a toroidal shapeacross the pair of bead cores 7 and a turn-up portion wound around eachbead core 7 from the inner side toward the outer side in the tirewidthwise direction then toward the outer side in the tire radialdirection. The number of plies and the structure of the carcass 4,however, are not limited to those in the aforementioned example in thepneumatic tire described herein. The bead filler 8 is disposed betweenthe main body portion and each turn-up portion of the carcass in thepneumatic tire of the example shown in FIG. 1.

In the tread portion 3 of the pneumatic tire of the example shown inFIG. 1, the belt 5 formed from two belt layers is disposed on the outerside in the tire radial direction of a crown portion of the carcass 4.The belt layers are steel cord layers coated with rubber and extendingto be inclined with respect to the tire equatorial plane E. The two beltlayers of the example shown in FIG. 1 are laminated such that steelcords constituting one belt layer intersect steel cords constituting theother belt layer with respect to the tire equatorial plane E, totogether constitute the belt 5. Although the belt 5 shown in FIG. 1 isformed from two belt layers, the number of the belt layers constitutingthe belt 5 may be three or more in the pneumatic tire disclosed herein.Although the pneumatic tire shown in FIG. 1 has the single beltreinforcing layer 6 disposed on the outer side in the tire radialdirection of the belt 5, the pneumatic tire described herein may lackthe belt reinforcing layer 6 or may have two or more belt reinforcinglayers 6.

While the belt 5 is shown as being symmetrical across the tireequatorial plane E, the tread portions on the left and right sides ofthe figure have different tread patterns about the tire equatorialplane, as shown in FIG. 1(A). In this case, hatched portions in FIG. 1(A) are groove portions 11, and regions extending between the tireequatorial plane E and respective outer ends in the tire width directionof the belt 5 represent tread halves HT, LT, respectively, where thetread half HT contains more groove portions 11, i.e., it has a highernegative ratio.

In the tire having such an asymmetrical tread pattern, the highernegative ratio of one tread half is preferably 20% to 60%, and the lowernegative ratio of the other tread half is preferably 10% to 50%.

In the pneumatic tire shown in FIG. 1, many short fibers 10 are fixed byan adhesive to at least a portion of a tire inner peripheral surface ofthe tread portion, namely, at least a portion of the inner liner 9 onthe side of the inner peripheral surface of the tire. Assuming that thetread portion is split into two tread halves HT, LT by the tireequatorial plane, one tread half HT with a higher negative ratio has ahigher proportion of short-fiber fixation area on the tire innerperipheral surface, as compared to the other tread half LT. When viewedin a widthwise section, the pneumatic tire has short fibers 10 fixedlyprovided on at least a portion of the tire inner peripheral surface ofthe tread portion. Thus, the short fibers 10 are provided on the innersurface of an air chamber formed when the tire is mounted on a rim. Theshort fibers 10 thus fixed to the tire inner peripheral surface absorbcavity resonance, and may reduce noise caused by the cavity resonancephenomenon.

In the tire inner peripheral surface, by setting the short-fiberfixation area ratio of the tread half HT with a higher negative ratio tobe higher than that of the tread half LT, the rigidity of the tread halfHT, which would otherwise be low if no short fibers are fixed, may beenhanced by the rigidity of the adhesive layer, and the imbalance ofrigidity between the tread halves HT and LT may be reduced, resulting ingood steering stability.

Examples of the short fibers 10 include short fibers of organicsynthetic fibers, inorganic fibers, regenerated fibers, natural fibersand the like. Examples of organic synthetic fibers include fibers madeof: polyolefin such as polyethylene, polypropylene, and polybutylene;aliphatic polyamide such as nylon; aromatic polyamide such as Kevlar;polyester such as polyethylene terephthalate, polyethylene naphthalate,polyethylene succinate, and polymethyl methacrylate; syndiotactic1,2-polybutadiene; acrylonitrile-butadiene-styrene copolymers;polystyrene; and copolymers thereof. Examples of inorganic fibersinclude carbon fiber, glass fiber and the like. Examples of regeneratedfibers include rayon, cupra, and the like. Examples of natural fibersinclude cotton, silk, wool, and the like.

In the pneumatic tire disclosed herein, it is preferred that the shortfibers 10 are fixed to the tire inner peripheral surface of the treadportion so that they are situated only in the tread half HT with ahigher negative ratio. This configuration may correct the unbalance ofrigidity between the tread halves HT, LT using a minimum amount ofadhesive.

In the pneumatic tire, it is also preferred that the short fibers 10 arefixed to the tire inner peripheral surface so that they are situatedeither in part of or throughout the tire side regions, which extend fromthe outer ends in the tire width direction of the tread portion 3 to theinner ends 1A in the tire radial direction of the bead portion 1,respectively. It is particularly preferred that the short fibers arefixed to the tire inner peripheral surface throughout the tire sideregions excluding the rim attachment portions, as shown in FIG. 1(B). Inthis way, fixing the short fibers 10 to the tire side regions may reducethe cavity resonance of the tire more easily without affecting thesteering stability thereof, than in the case of a tire without fixingshort fibers to these regions.

In the pneumatic tire disclosed herein, the short fibers are disposedpreferably at a density of 100 fibers/cm² or more in the region wherethe short fibers are fixed to the tire inner peripheral surface in thetire side regions. By doing so, a reduction effect of cavity resonancesound can surely be obtained. From the viewpoint of obtaining an evenbetter cavity resonance sound reduction effect, the short fibers aredisposed more preferably at a density of 500 fibers/cm² or more, andparticularly preferably at a density of 1,000 fibers/cm² or more and20,000 fibers/cm² or less.

In another preferable example of the pneumatic tire, the average lengthof the short fibers is 0.5 mm to 10 mm. By setting the length of shortfibers to 0.5 mm or more, the effect of reducing the cavity resonancesound can be sufficiently obtained. On the other hand, by setting theaverage length of short fibers to 10 mm or less, it is possible to avoidthe problem of tangling between short fibers which leads to aninsufficient expression of noise-absorbing effect. From the sameviewpoint, the average length of the short fibers is particularlypreferably 2 mm to 8 mm.

The area where short fibers are fixed is preferably 25% or more,particularly preferably 50% or more, and further preferably 70% or moreof the area of the tire inner peripheral surface. In this respect, theshort-fiber fixation area ratio in the tread half HT with a highernegative ratio is higher than that in the other tread half LT.Specifically, the short-fiber fixation area ratio in the tread half HTis preferably 50% or more, and particularly preferably 70% or more. Bysetting the short-fiber fixation area ratio within the tread half HT tobe 50% or more, the cavity resonance can surely be reduced.

To balance the rigidity between the tread halves, the short-fiberfixation area ratio in the other tread half LT is preferably 0% to 25%.

In another preferable example of the pneumatic tire, the averagediameter of the short fibers is 1 μm to 500 μm. In this way, threadbreakage in a production process of the short fibers is suppressed, anda decrease in productivity of the short fibers can be suppressed.Further, it is possible to suppress the increase in rolling resistancecaused by the increase in tire weight, and suppress the decrease in thefuel consumption rate of a vehicle on which the tires are mounted.

In the pneumatic tire, the ratio (L/D) of length (L) to diameter (D) ofthe short fibers is preferably in the range of 5 L/D 2000. With a ratio(L/D) of length to diameter of less than 5, the effect of reducingcavity resonance becomes small. On the other hand, with a ratio (L/D) oflength to diameter exceeding 2,000, tangling may be caused between theshort fibers and lead to an insufficient expression of noise-absorbingeffect.

In the pneumatic tire, it is preferred that the region where the shortfibers are fixed is formed by multiple groups of short fibers, and thatthe groups of short fibers are fixed independently from each other. Bydiscontinuously providing regions where short fibers are fixed, even ifan adhesive layer comes off, the area of coming off is kept very small,and the effect of suppressing cavity resonance can be maintained.

A method of producing the aforementioned pneumatic tire disclosed hereincomprises: applying an adhesive to at least a portion of the tire innerperipheral surface of the tread portion; and adhering short fibers tothe part to which the adhesive has been applied. In the adhering theshort fibers, one of the tread halves with a higher negative ratio has ahigher short-fiber fixation area ratio than that of the other.

According to the tire producing method disclosed herein, it is possibleto efficiently produce a pneumatic tire that is capable of preventingdeterioration of steering stability and suppressing the generation ofcavity resonance.

According to the tire producing method, a pneumatic tire capable ofproducing an excellent noise-absorbing effect as mentioned above may bemanufactured by first applying an adhesive to a short-fiber fixationpart situated on at least a portion of the tire inner peripheral surfaceof the tread portion, then adhering short fibers 10 to the portion towhich the adhesive has been applied.

The adhesive to be used is not limited to a particular type and anyadhesive can be used. A polyurethane resin adhesive, an acrylic resinadhesive, an epoxy resin adhesive, and the like are suitably used. Thethickness of the formed adhesive layer is also not particularly limitedas long as it does not exceed the length of short fibers. A thickness of50 μm to 500 μm is preferable.

In the method of producing the pneumatic tire disclosed herein, theshort fibers 10 are preferably adhered to the tire inner peripheralsurface by electrostatic flocking after the applying process i.e. duringthe adhering process. The short fibers 10 can be adhered to the tireinner peripheral surface by various methods. However, by applying anelectrostatic flocking process, the short fibers 10 can easily be fixedto the tire inner peripheral surface in a state where the short fibers10 stand upright thereon, and a pneumatic tire that enables obtaining anoise-absorbing effect can be efficiently produced.

Electrostatic flocking is a processing technique of electricallycharging short fibers and attaching the short fibers, by electrostaticforce, perpendicularly to an object with an adhesive applied thereto inadvance. Therefore, it enables uniformly attaching short fibers to anobject surface having a complicated shape and is suitable for attachingthe short fibers 10 to a tire inner peripheral surface having athree-dimensional curvature.

The pneumatic tire disclosed herein is generally assembled onto a rim,and as a tire-rim assembly, it is mounted on a desired vehicle for use.In order to further enhance the effect of reducing cavity resonance, theaforementioned short fibers may be fixed to a part of or the whole rim.

EXAMPLES

Although the disclosure will be described below in further detail withreference to examples, the disclosure is not intended to be limited inany way to the following examples.

Example 1 and Comparative Examples 1 and 2

Tires of the same specification having the tread pattern as shown inFIG. 1 were prepared with or without short fibers made of nylon beingattached to a predetermined region therein by flocking. For each tire,cavity resonance and steering stability were measured as describedbelow. The tires used were of tire size 255/35R20 with the structure asshown in FIG. 1. Specifically, the tread portion of each tire is splitinto two sides, serial side (tread half HT) and opposite serial side(tread half LT), by the equatorial plane E, and the negative ratio onthe serial side is set to be 48% and the negative ratio of the oppositeserial side is set to be 26%. Rims of 8.5J-20 were used. Note that themaximum width BW in the tire width direction of each belt layer is 78%of the maximum width of the tire.

Example 1 is a tire as shown in FIG. 1(B) that has short fibers attachedby flocking to regions of the inner peripheral surface, ranging from theequator plane E to the inner ends 1A in the tire radial direction of thebead portion 1 on the serial side (excluding the rim attachmentportions). Comparative example 1 is a tire that has no short fibersprovided on the tire inner peripheral surface, and comparative example 2is a tire that has short fibers attached by flocking to the entire tireinner peripheral surface excluding the rim attachment portions (FIG. 2).The conditions of short fibers used in the short-fiber fixation regionswere consistent among all the tires, and were set as follows: density:2,000 short fibers/cm²; average length: 4 mm; average diameter: 50 μm;and short-fiber fixation area ratio in short-fiber fixation regions:100%. For each tire of example 1 and comparative examples 1 and 2,cavity resonance and steering stability were evaluated as follows.

<Cavity Resonance>

Each sample tire was assembled onto a rim of 8.5J-20, and rotated underthe conditions of internal pressure of 260 kPa, tire load mass of 5.0kN, and speed of 80 km/h, using a drum tester equipped with an iron drumhaving an iron plate surface with a diameter of 1.7 m, as shown in FIG.3, to measure and evaluate the generated vertical tire axial force usinga wheel force sensor. The frequency spectrum of the results is shown inFIG. 4. In the spectrum shown in FIG. 4, a lower peak at 210 Hzrepresents a larger reduction in cavity resonance of the tire. From thespectrum shown in FIG. 4, reduction in the peak of each sample tirecompared to the tire of comparative example 1 was determined (in dB).

<Steering Stability>

As an index of cornering characteristics of a tire which is dominantover steering characteristics of a vehicle, CP (cornering power)measured using a flat-belt type testing machine was evaluated. Eachsample tire was assembled onto a rim of 8.5J-20, then rotated under theconditions of inner pressure of 260 kPa, load mass of 5.0 kN, and speedof 80 km/h, using a flat-belt type testing machine, to measure thestress produced in the tire at slip angles of ±0 degrees, 0.5 degrees,and 1 degree, respectively, and to determine the inclination (kgf/deg)at 0 degrees. With CP of 1.5 kN/deg or more, steering stability isconsidered sufficient.

TABLE 1 Reduction in peak at around Steering Stability CP 210 Hz [dB][kN/deg] Example 1 5.7 1.55 Comparative Reference 1.40 Example 1Comparative 6.1 1.41 Example 2

In FIG. 4, peaks at around 210 Hz result from cavity resonance, and itcan be seen that the tire of example 1 yielded a large reduction,approximately 4 dB, as compared to comparative example 1. It can also beseen that example 1 exhibited improved steering stability as compared tocomparative examples 1 and 2.

REFERENCE SIGNS LIST

1 Bead portion

1A Inner end in tire radial direction of bead portion

2 Sidewall portion

3 Tread portion

4 Carcass

5 Belt

6 Belt reinforcing layer

7 Bead core

8 Bead filler

9 Inner liner

10 Short fiber

11 Groove portion

BW Maximum width in tire widthwise direction of belt layer

E Tire equatorial plane

HT, LT Tread halves

The invention claimed is:
 1. A pneumatic tire comprising a tread portionand tire side regions, the tread portion having an asymmetrical treadpattern and a pair of tread halves, the tread halves extending between atire equatorial plane and respective outer ends in the tire widthdirection of the tread portion, respectively, and having differentnegative ratios, wherein the tread portion has short fibers fixed to atleast a portion of a tire inner peripheral surface of the tread portion,the short fibers are situated only in one of the tread halves with ahigher negative ratio, and the tread half with a higher negative ratiohas a short-fiber fixation area ratio of 50% or more, and wherein shortfibers are also fixed to at least a portion of a tire inner peripheralsurface of the tire side regions.
 2. A method of producing the pneumatictire as recited in claim 1, the method comprising: applying an adhesiveto at least a portion of the tire inner peripheral surface of the treadportion of the one of the tread halves with a higher negative ratio andat least a portion of the tire inner peripheral surface of the sideregions; and adhering short fibers to the portions to which the adhesivehas been applied, so that the short fibers are situated only in the oneof the tread halves with a higher negative ratio and the side regions,and wherein one of the tread halves with a higher negative ratio has ashort-fiber fixation area ratio of 50% or more.
 3. The method ofproducing the pneumatic tire according to claim 2, wherein after theapplying, the short fibers are provided on the tire inner peripheralsurface by electrostatic flocking.
 4. The method of producing thepneumatic tire according to claim 2, wherein a ratio (L/D) of length (L)to diameter (D) of the short fibers is in a range of 5≤L/D≤2000.
 5. Thepneumatic tire according to claim 1, wherein a ratio (L/D) of length (L)to diameter (D) of the short fibers is in a range of 5≤L/D≤2000.
 6. Thepneumatic tire according to claim 1, further comprising an adhesivelayer for fixing the short fibers on the tire inner peripheral surface.